Due to various advantages such as a high data-transmission rate, a high beamforming gain and a high spatial resolution, massive MIMO communications have attracted considerable interest for future deployment in mobile communication systems. In a massive MIMO system, a transmitter has a very large number of transmit antennas, e.g., greater than 100. In estimating a massive MIMO channel, the large number of transmit antennas often leads to a high computation requirement and a need for a lot of training resources, e.g., orthogonal time/frequency resource, in channel estimation. It is desirable to reduce these demands in operations in mobile communication systems.
US20130182594 discloses a reduced-complexity channel-estimation technique by grouping the transmit antennas into groups for training. By reducing the number of antennas for estimation in each group, channel estimation requires less computation. However, spatial correlations are not taken into account to improve accuracy in channel estimation. Reduced-complexity techniques disclosed by US20130272263 and US20140254702 also have an estimation-accuracy issue since channel correlations are not taken into account. U.S. Pat. No. 8,837,621 teaches transmitting pilot reference signals on only a subset of antennas and using spatial interpolation to obtain channel estimates for other antennas. However, high estimation error results when spatial correlations among the antennas are not adequately high.
There is a need in the art to have a technique for estimating the massive MIMO channel with improved estimation accuracy while maintaining low requirements in computation and in training resources.